Insulated Glazing Properties_Simplified VS Manufacturer Data

[claudiobo]

Dear all,

I would need an explanation regarding the definition of insulated glazing properties in IES-VE.
I made a test modeling 3 separated spaces with same size, same exposure and an only window exposed to south (without any shading/obstruction) with different solar properties:

-Insulated Glazing 1 (IG1) is completely clear to solar transmission (T=g_value=100%, out_R=in_R=0)
-IG 2 is modeled to obtain the same g_value of the manufacturer IG (IG 3), but in a simplified method (T=g_value=34%, out_R=1-g_value, in_R=0)
-IG 3 is modeled with manufacturer data: g_value=34% (T=32%, out_R=34%, in_R=34%).

Even if the g-values of IG2-IG3 are the same (and the total SC are very similar), comparing the solar gain results (in W, on hourly base) of a summer day (obtained by ApacheSim):
- Space 2 solar gains are exactly the 34% of those of Space 1’s (IG1, g_value=100%)
- Space 3 solar gains vary between 23-26% of those of Space 1’s
- Space 3 solar peak load is around the 50% of Space 2’s.

Comparing the solar gain results along the simulation year (in kWh):
- In winter months, Space 3 solar energy gain is about the 75% of Space 2’s.
- In summer months, Space 3 solar energy gain is about the 60% of Space 2’s.

Consequently, the question is simple: how should I model an insulated glazing?
I read the Construction Database User Guide (especially the Hints & Tips), but I’ve not found any answer.

Thank you in advance.
c